多态

1.虚函数：

不同对象面对相同的操作会体现出各自不同的地方

静态多态：早绑定，名字相同，参数不同，函数重载；同一个对象接受不同的操作

Class Rect{

public:

 int calArea(int width);

 int calArea(int width,int height);

}

动态多态：晚绑定，以封装和继承为基础，；不同对象下达相同的操作，产生不同的实现；如何体现出这个多态

class Shape{
  public:
     double calcArea(){
      cout<<"calcArea"<<endl;
  }
};

//圆类，继承了Shape类
class Circle :public Shape{
    public:
             Circle(double r);
             double calcArea();
    private:
             double m_dR;
};
double Circle::calcArea(){
   return 3.14*m_dR*m_dR;
}

//矩形类，继承了Shape类
class Rect : public Shape{
      public:
               Rect(double width,double height);
               double calcArea();
      private:
                m_dWidth;
                m_dHeight;
};
double Rect:: caclArea(){
     return   m_dWidth* m_dHeight;
}

int main(void){
   Shape *shape1 = new Circle(4.0);//打印的是calcArea
   Shape *shape2 = new Rect(3.0,5.0);//打印的是calcArea
   ...
   return 0;
}

class Shape{
   public:
      Shape();
      virtual double calcArea();//实现多态的函数定义为virtual函数
      ~Shape();
};
Shape::Shape(){
    cout<<"Shape()"<<endl;
}
Shape::~Shape(){
    cout<<"~Shape()"<<endl;
}
double Shape:: calcArea(){
    cout<< "Shape->calcArea"<<endl;
}

class Circle:public Shape{
public:
      Circle(double r);
      virtual double calcArea();//可加可不加，最好加
      ~Circle();
protected:
      double m_radius;
};
Circle::Circle(double r){
    m_radius = r;
    cout<<"Circle"<<endl;
}
Circle::~Circle(){
    cout<<"~Circle"<<endl;
}
double Circle::calcArea(){
    cout<<"Circle->calcArea()"<<endl;
    return 3.14*m_radius*m_radius;
}

class Rect:public Shape{
public:
    Rect(double width,double height);
    ~Rect();
    virtual double calcArea();//可加可不加，最好加
protected:
    double m_dWidth;
    double m_dHeight;
};
Rect::Rect(double width,double height){
    m_dWidth=width;
    m_dHeight=height;
    cout<<"Rect()"<<endl;
}
Rect::~Rect(){
    cout<<"~Rect()"<<endl;
}
double Rect::calcArea(){
     cout<<"Rect->calcArea()"<<endl;
    return m_dWidth*m_dHeight;
}


//使用，注意和上面的代码作对比
#include<iostream>
#include<stdlib.h>
#include"Shape.h"
#include"Circle.h"
#include"Rect.h"
using namespace std;

int main()
{
    Shape *p1 = new Circle(2);
    Shape *p2 = new Rect(2,3);

    p1->calcArea();//调用的应该是Circle的函数
    p2->calcArea();//调用的应该是Rect的函数

    delete p1;
    p1 = NULL;
    delete p2;
    p2 = NULL;
   //Worker *p = new Worker();
    //delete p;
   // p = NULL;
   // system("pause");
    return 0;
}

/*输出结果
Shape()
Circle
Shape()
Rect()
Circle->calcArea()
Rect->calcArea()
~Shape()
~Shape()
*/